Asking here because I get notified if you reply: why rockettes? Beside the obvious cool factor and the vague notion that euhumanists can't just do things normally and have to have an extra layer of complexity, is there like a... practical advantage to having a gun that shoots rockets vs one that shoots bullets? They don't seem guided or explosive, and without fins would they be more accurate or reach longer distances than a single-impulse munition?
My rationale for this is both aesthetic (retro-futurism) and internal world logic.
First, the internal logic of the world.
The Euhumanists have spent centuries, presumably, using beam weapons for small arms (like star trek). If they were stuck without reliable beam weapons (because of limited power sources, manufacturing capabilities, etc, like in "the grand tour"), and were developing their industrial capacities from a very limited base, circumstances would possibly force them to essentially re-invent the gun.
Given their own history as space-faring people, I was thinking that the rocket would probably be their most direct reference for a combustion-driven kinetic device - so having them develop an awkward micro-rocket, instead of first developing muskets or cartridge ammunition, felt suitably unique, clunky and weird for the world.
Also, in researching "caseless" ammunition of this type, like russian VOG launched grenades, the gyrojet, the italian 9mm AUPO round, and, the granddaddy of them all, the 1800s ROCKET BALL (see below image), it was interesting seeing all the other methods of containing projectile and gunpowder in one discrete unit.
The rocket ball came about in 1848 and was my biggest inspo for this, but the utterly magical and deranged GYROJET missile-bullet was up there too. If you search youtube for gyrojet firing footage, its completely fascinating!
This is all to say, though, that aesthetics and the idea of this colony fumbling their way into firearms came first. This style of ammo doesnt have much in the way of practical advantages over modern cartridges, but modern cartridges also just felt WAY too anachronistic to throw into this setting. But it has been a very fun research rabbit hole for me to clamber down!
